Fuel tanks assembled from a two plastic shells are known, and may comprise a stabilizing column or wall in the internal volume of the tank in order to limit deformations of the tank. Traditionally fuel systems in passenger vehicles are designed to hold a specific amount of liquid fuel at a pressure essentially the same as the ambient pressure. With the introduction of Hybrid vehicles and more specifically Plug in Hybrids, which are designed such that they could potentially go several months without using fuel, it is in the interest of the system designers to hold pressure inside the fuel tank to limit the emissions that could potentially bleed through the activated carbon canister due to diurnal cycles. In addition, holding pressure ensures that the composition of the fuel stays the same during storage. However, the tanks must be made resistant to this internal pressure. Therefore tank reinforcement can be realized by linking two opposite tank surfaces with each other using an internal pillar.
It is known to form a stabilizing pillar or wall using a first pillar or wall part that is integrally moulded with the first plastic shell and a second pillar or wall part that is integrally moulded with the second plastic shell. When welding the first shell along its perimeter to the second shell, at the same time, the first pillar or wall part may be connected (e.g. by welding or by a snap connection, see DE 102009036911) to the second pillar or wall part in order to form the stabilizing pillar or wall in the internal volume of the tank. In the case of welding this is a complex and delicate operation as the first and second pillar or wall parts are not easily accessible. The reinforcement pillars or walls are typically at a distance from the perimeter welding path of the first and second shells, resulting in the need for complex welding tools. Also, a very delicate controlling of the welding operation is required as the dimensional tolerance on the moulded first and second shells may lead to interference between the first and second shell at a number of locations and lack of contact at a number of other locations.